1. Field of the Invention
The present invention relates to a process for producing continuously a methacrylimide group-containing polymer excellent in transparency and mechanical properties.
2. Description of the Prior Art
Since methacrylic resins are excellent not only in transparency but also in weather resistance and mechanical properties they have become to be used in various end uses as in high-performance optical materials, decorative materials, automobiles, and electric appliances. Recently, the methacrylic resins are often used under high temperature conditions, and therefore not only excellent transparency but also high heat resistance is increasingly sought for the methacrylic resins in the market. In other words, transparent resins that can keep excellent optical characteristics for a long period of time under high temperature conditions is in need.
As heat resistant transparent resins, imide group-containing polymers are known. To produce such polymers, there have been proposed, for example, (1) a process disclosed in U.S. Pat. No. 2,146,209 wherein a polymer of acrylic acid, methacrylic acid or their ester, and a primary amine, ammonia or a compound capable of liberating a primary amine are heated to react in the presence of a solvent, (2) a process disclosed in U.S. Pat. No. 3,284,425 wherein a methyl methacrylate polymer is reacted with a primary amine in the presence of water, and (3) a process disclosed in U.S. Pat. No. 4,246,374 wherein an acrylic polymer, and ammonia or a primary amine are reacted in an extruder.
However, since the boiling point of the solvent used in the process (1) mentioned above is high, the process (1) has defects that complete removal of the solvent from an imidized polymer produced is hard on a commercial scale, and the resulting imidized polymer is colored so that the transparency of the polymer is low. In the process (2) mentioned above, since a primary amine is reacted in the presence of water, hydrolysis of methyl methacrylate segments occurs, so that it is difficult to obtain an imidized polymer having a high heat resistance, and it is difficult to effect a uniform imidization reaction. Further, since the process (3) mentioned above includes an imidization reaction wherein a highly viscous polymer and a gaseous imidizing agent are reacted, it is difficult to effect a uniform imidization reaction, so that it is hard to obtain a uniformly imidized polymer.
Therefore, although the imidized polymers produced by the process explained above are improved in heat resistance, such disadvantages are involved in the processes that the transparency of the resulting imidized polymers is poor, the molecular weight of the polymer is substantially lowered, and the imidization reaction is not uniform, when the imidized polymers are to be produced in commercial scale.